Principles

A landslide is the gravitational movement of a mass of rock, earth or debris down a slope. Landslides are usually classified on the basis of the material involved (rock, debris, earth, mud) and the type of movement (fall, topple, avalanche, slide, flow, spread). Thus, the generic term landslide also refers to mass movements such as rock falls, mudslides and debris flows. Volcanic mudflows and debris flows are also called lahars.

Shallow landslides usually involve only the soil layer and upper regolith zone, while deep-seated landslides additionally involve bedrock at higher depth. Landslide volume can vary from some tens of cubic metres to several cubic kilometres for giant landslides, while landslide speed may range from a few centimetres per year for slow-moving landslides to tens of kilometres per hour for fast, highly destructive landslides. According to the state of activity or movement, existing landslides can be classified as active, dormant (potentially reactivated) or inactive (often relict or fossil).

Landslides are generally induced when the shear stress on the slope material exceeds the material’s shear strength. The occurrence and reactivation of landslides is conditioned by a number of terrain and geo-environmental factors related to bedrock and soil properties, weathering conditions, jointing and structure, slope morphology, land cover/use, surface and ground water flow, etc.

Landslides can be triggered by natural physical processes such as heavy or prolonged rainfall, earthquakes, volcanic eruptions, rapid snow melt, slope undercutting by rivers or sea waves and permafrost thawing. They can also be triggered by man-made activities such as slope excavation and loading (e.g. road and buildings construction, open-pit mining and quarrying), land use changes (e.g. deforestation), rapid reservoir drawdown, irrigation, blasting vibrations, water leakage from utilities, etc, or by any combination of natural and/or man-induced processes.

Landslide in Veneto, Italy

Impacts

Landslides are a major hazard in most mountainous and hilly regions as well as in steep river banks and coastlines. Their impact depends largely on their size and speed, the elements at risk in their path and the vulnerability of these elements. Every year landslides cause fatalities and result in large damage to infrastructure (roads, railways, pipelines, artificial reservoirs, etc.) and property (buildings, agricultural land, etc.).

Large landslides in mountainous areas can result in landslide dams blocking river courses. These natural dams cause valley inundation upstream and can be subsequently breached by lake water pressure, hence generating deadly flash floods or debris flows downstream. Submarine and large coastal cliff landslides can trigger tsunami, as can landslides in lake and reservoir shores.

Landslides can also affect mine waste tips and tailings dams and landfills, causing fatalities and contaminating soils and surface and ground water.

In areas affected by landslides, these are a major source of soil erosion and sediment yield to valleys and rivers.

However, most statistics on natural disasters underestimate the impacts from landslides as they often do not separate them from other triggering or concurrent natural hazards such as storms, floods or earthquakes.

Landslides in Europe

Landslide occurrence

Landslides occur in many different geological and environmental settings across Europe. For example, large rockfalls, rockslides, rock avalanches and debris flows dominate in the Alps and steep slopes in other mountain ranges; slides and flows abound in flysch belts of Slovakia, Czech Republic, Poland, Slovenia, Italy, Spain, France and other countries; slides of various types are numerous on cliffs and steep slopes in Southern and Eastern England’s coast and Bulgaria’s Northern Black Sea coast; shallow slides and mudflows occur on Ireland’s peat slopes; slides and lateral spreads do as well on gentle slopes in quick clays in Sweden and Norway; flows and slides also typically occur in clay-rich sediments and sedimentary sequences in Tertiary basins as well as on river banks, etc.

Intense and/or long-lasting rainfall represents the most frequent trigger of landslides in continental Europe. However, earthquakes are also responsible for some large landslides. Human activities are also the cause of many slope failures in infrastructure and built-up areas.

Landslides are a major factor of landscape evolution in mountainous and hilly regions in Europe. In addition to causing extensive erosion and sediment yield in these regions, large landslides have been responsible for the creation of many lakes in the Alps and other mountain ranges by damming river valleys. Examples of this include the lakes of Santa Croce, Antrona (formed in 1642), Alleghe (formed in 1771) and Scanno in Italy, Eibsee and Obersee in Germany, Blindsee in Austria, Vallon in France (formed in 1943), Lacul Rosu in Romania (formed in 1837), and Poschiavo, Klöntal, Derborence (formed in 1749), Sils, Silvaplana, Oeschinen and Davos in Switzerland. Most landslide dams, however, have often formed temporary lakes that have later breached the dam causing catastrophic flash floods and debris flows. Today, hills in some alpine valley bottoms are remnants of large deposits from giant landslides (e.g. from prehistoric rock avalanches with volumes even in excess of 1 km3 such as Flims, Sierre and Tamins in Switzerland, Köfels, Fernpass and Tschirgant in Austria, etc.). Many landslide-dammed lakes have been progressively filled with sediments, thus also modifying the valley environment. Unfortunately, the hazard of river damming from landslides still exists in these regions: outstanding examples are those of La Clapičre and Séchilliene rockslides in the French Alps, whose potential movement acceleration threatens communities located far from the unstable slopes. On the other hand, landslides in steep coastal areas including cliffs accelerate erosion and subsequent cliff retreat by sea waves.

Giant subaerial landslides are not exclusive of the Alps. They have also occurred in prehistoric times in areas such as southern Crimea in Ukraine, Isle of Skye in UK, and especially in the Canary Islands, Spain. In the latter, a number of huge debris avalanches entered the ocean triggering tsunami. Evidence of large tsunami are also found in Scotland and other coastal areas bordering the Norwegian Sea, mainly attributed to the Storegga submarine megaslide (ca. 3,500 km3) off the west coast of Norway. In the Mediterranean, landslide-triggered tsunami have been observed dominantly in the Corinth Gulf, Greece, and the Aeolian Islands, Italy. Recent examples include the local tsunami caused by the collapse of the Nice airport embankment in 1979 and the small to moderate tsunami produced by a landslide on the Stromboli Island flank in 2002.

Nowadays, population growth and expansion into landslide-prone areas is raising landslide risk in Europe. In addition, an increase of landslides associated to extreme rainfall events is expected in the future due to climate change.

Major historic landslide disasters

There is a long record of landslide disasters in historical and recent times in Europe causing many fatalities and high economic losses. Major disasters include, among others, those of Goldau (1806), Elm (1881) and Gondo (2000) in Switzerland; Piuro (1618), Antronapiana (1642), Roccamontepiano (1765), Monte Antelao (1814, 1925), Vajont (nearly 2000 killed by reservoir wave caused by man-induced landslide in 1963) and, more recently, Valpola (1987), rainfall-triggered multi-landslide events in Piedmont region (1994), Sarno and Quindici (1998) and Messina (2009), and the train accident at Laces (2010), all in Italy; Granier (1248) and Plateau d’Assy (1970) in France; Felanitx (1844), Azagra (1874) and Granada province (earthquake-triggered multi-landslide event, 1884) in Spain; Mount Dobratsch (1348) in Austria; Getĺ (1918) and Tuve (1977) in Sweden; Verdalen (1893) and landslide-triggered local tsunami at Loen (1905, 1936) and Tafjord (1934)in Norway.

In addition, landslides occurring in mine waste tips and tailings dams have been the origin of the catastrophes of Sgorigrad, Bulgaria (1966), Aberfan (1966) in Wales, UK, and Stava (1985) in Trento, Italy.

Lessons learnt from the management of a number of landslide disasters occurred in Europe in the 1990s and early 2000s are reported here

Landslides and the EU Soil Thematic Strategy

Landslides are one of the soil threats considered in the EU Thematic Strategy for Soil Protection and the related Proposal for a Soil Framework Directive. The Strategy calls for actions and means for the protection and sustainable use of soils as a physical platform on which human activities are developed. The proposed Directive, in turn, will be the Strategy implementing tool. This will mainly require to identify landslide and other soil threat risk areas in the European
Union, set risk reduction targets for those areas and establish programmes of measures by Member States to achieve them.

JRC activities

The JRC provides scientific and technical support to the European Commission Services for the implementation of the EU Thematic Strategy for Soil Protection, both through its own work activities and in collaboration with national research organizations, mapping agencies and academia. Our main activities and expertise include harmonisation of methods for landslide mapping and zoning in Europe (inventory, susceptibility, hazard and risk) at various scales, development of satellite, airborne and ground-based remote sensing techniques for landslide mapping and long term monitoring, analysis of lessons learnt from management of past landslide disasters, and spatial database management. Find more information here.

Collaborative activities are carried out in various frameworks:

European Landslide Expert Group. Founded and coordinated by JRC, this group includes experts from a number of national geological surveys, national research institutes, and universities. The group is currently developing models for landslide susceptibility assessment and mapping at European and national scales (see publications).

International Consortium on Landslides (ICL),
an international non-governmental scientific organisation supported by UNESCO, UN/ISDR, FAO, WMO and intergovernmental programmes. ICL promotes and coordinates collaborative research and expertise, as well as capacity building, on landslide risk reduction.
JRC participates in ICL's International Programme on Landslides (IPL) and other activities such as the organisation of World Landslide Forums.
The JRC’s Institute of Environment and Sustainability (IES) has been awarded the status of World Centre of Excellence on Landslide Disaster Reduction for the period 2011-2014 in the field of research on landslide risk management harmonisation in support to European Union policy making.

European Centre on Geomorphological Hazards (CERG) , a specialized research network of the Council of Europe’s EUR-OPA Major Hazards Agreement co-operation platform. CERG promotes international scientific cooperation and training on prevention of geomorphological and geohydrological hazards and risks, especially landslides, gravitational flows and floods.

European Landslide Susceptibility Map (ELSUS1000) v1

ELSUS1000 version 1 shows levels of spatial probability of generic landslide occurrence at continental scale. It covers most of the European Union and several neighbouring countries. Basically, the map has been produced by regionalizing the study area based on elevation and climatic conditions, followed by spatial multi-criteria evaluation modelling using pan-European slope gradient, soil parent material and land cover spatial datasets as the main landslide conditioning factors. In addition, the location of over 100,000 landslides across Europe, provided by various national organizations or collected by the authors, has been used for model calibration and validation. Additional information is provided in the references below and the metadata.

The map has been produced jointly by the Federal Institute for Geosciences and Natural Resources (BGR, Hannover, Germany), the Joint Research Centre (JRC, Ispra, Italy), the Institute of Physics of the Globe (CNRS-EOST, Strasbourg, France), and the Research Institute for Hydrogeological Protection (CNR-IRPI, Perugia, Italy), as part of the work of the European Landslide Expert Group, with contributions from other members of the Group.

The map is available to download together with ancillary spatial datasets used for landslide susceptibility modelling, or produced for referencing to administrative regions and for evaluation of the confidence level of the classified landslide susceptibility.